Electronic Nature of New Ir(III) Complexes: Linear Spectroscopic and Nonlinear Optical Properties

Abstract

Comprehensive investigations of the linear and nonlinear optical properties of new Ir(III) complexes [Ir(pbt) 2 (dbm)] ( 1 ), [Ir(pbt) 2 (dmac)] ( 2 ), and [Ir(pbt) 2 (minc)] ( 3 ) (pbt = 2-phenylbenzothiazole; dbm = dibenzoyl methane; dmac = (1E,4Z,6E)-1,7-bis(4-(dimethylamino)phenyl)-5-hydroxyhepta-1,4,6-trien-3-one; minc = (1E,4Z,6E)-5-hydroxy-1,7-bis(1-methyl-1H-indol-3-yl)hepta-1,4,6-trien-3-one) are reported, including photostability, two-photon absorption, and femtosecond transient absorption spectroscopy. The steady-state and time-resolved spectral properties of 1 – 3 revealed the electronic nature of the absorption bands, and photoluminescence emission of 2 and 3 shows both fluorescence and phosphorescence processes occurring simultaneously in liquid solution at room temperature. This unusual behavior of 2 and 3 can be explained by a dual-minimum potential surface of the excited electronic state resulting in two independent fluorescence and phosphorescence emission channels. The degenerate 2PA spectra of 1 – 3 were obtained by open aperture Z-scans with a femtosecond laser, and maxima values of 2PA cross sections up to ∼350 GM were observed. Ultrafast relaxation processes of 1 – 3 were investigated by femtosecond transient absorption, and the characteristic times for triplet formation were determined to be <500 fs for 1 and ∼2 ps for 2 and 3 in a nonpolar medium.